Screw head



Nov. 21, 1939.

c. G. HOLT SCREW HEAD Filed July 19, 1938 Patented Nov. 21, 1939 UNITEDSTATES SCREW Clarence G. Holt,

HEAD

Melrose, Mass.

Application July 19, 1938, Serial No. 220,024

Claims.

This invention relates to improved screw head adapted to be engaged by aspecial complementary tool for rotation of the screw.

It is an object of the invention to provide a screw head which cannot beoperatively engaged by an ordinary screwdriver. It is a further objectof the invention to provide slots or recesses in the head so shaped asto minimize slippage of the tool and to afford an eificient leverage forrotation of the screw.

For a more complete understanding of the invention, reference may be hadto the following description of certain embodiments thereof, and to thedrawing, of which Figure 1 is a perspective view of a round-headed screwembodying the invention.

Figure 2 is a plan view of the same.

Figure 3 is a sectional view on the line 3-3 of Figure 2.

Figure 4 is a plan view of a flat-headed screw embodying the invention.

Figure 5 is a sectional view on the line 55 of Figure 4.

Figure 6 is a sectional view of a screw with an oval head.

Figure 7 is a sectional view of a screw with a binding head.

Figure 8 is a plan view of a fiat-headed screw with modified grooves orslots therein.

Figure 9 is a section on the line 99 of Figure 8.

Figure 10 is a sectional view of a screw with an oval head havingmodified grooves or slots therein.

Figure 11 is a perspective view of a tool for use with screws such asare illustrated in Figures 3, 6, 7 and 9.

The invention as illustrated is embodied in screw heads having thecustomary shapes or surface contours, some one oflwvhich is found onpractically all screws now on the market.

The screw shown in Figure 1 has a head l0 which is characterized by aplurality of slots or grooves extending radially from an unrecessedcentral surface portion I4 which lies in the contour of the screw head.Because of this central surface portion, the screw cannot be operativelyengaged by an ordinary screwdriver but must be rotated by a specialtooIH having complementary lugs or ridges l5 adapted to fit into thegrooves or slots l2. As indicated inFigures 1 and 2, it is preferred toemploy four slots l2 in order to give ample purchase onthe screw headfor the tool without unduly weakening the head itself by the removal oftoo much material, but

a greater or lesser number of slots may be employed. As shown in Figure2, the side walls of each slot are parallel. Thus the side walls of-each of the lugs 15 are parallel. This detail of structure is of greatpractical importance in that 5 slots of this kind having parallel sidewalls are more securely engaged by a complementary tool than are slotshaving diverging side walls. Thus in the case of the screw headsillustrated on the drawing, there is minimum possibility of slipping 10of the tool when the screw is being rotated thereby. The lugs l5 arepreferably made of such thickness as to have a frictional fit in theslots. By using a cold-forging process in making the screws, the slotscan be made with a high degree 5 of accuracy to have a uniform width.Hence the frictional fit serves to hold the screw head in the end socketof the tool so that the screw is supported by the tool when the lugs arepushed into the grooves. In the screw illustrated in Figures l, 2 and 3,the bottom of each slot starts flush with the central area l4 and slopesradially outward and downward in a straight line therefrom but leaves acontinuous shoulder l6 under the head of the screw. The outward anddownward slope of the groove bottoms serves to center the tool when itis thrust against the screw head.

Figures 4 and. 5 illustrate a flat-headed screw in which the head 20 hasa plane upper surface interrupted by four grooves 22 which extend froman unrecessed central surface portion 24 nearly to the peripheral edge26 of the head. Since these slots do not extend all of the way to thisedge, the edge is unbroken and forms a complete circle which lies in acommon plane with the central portion 24. The bottom of each slot slopesdownwardly toward the periphery of the head, as indicated in Figure 5,for most of the length of the slot, and then slopes upwardly to itsouter end adjacent to the edge 26 of the head.

Thus the deepest point 28 of each slot comes as far from the axis of thescrew as is possible without breaking the continuity of the edge 26 orof the conical under face 30 of the head. This results in a maximum armof rotation for each of the driving lugs of a complementary tool.

Figure 6 illustrates in section a screw having an oval head, that is, ahead with a curved contour on top and a conical contour underneath. Thecentral area 42 is unrecessed, that is, it lies in 60 the contour of thetop and t e slots 44 extend radially therefrom toward the peripheraledge 46 of the head. a The side walls of each of these slots areparallel, and the bottom slopes downwardly toward the edge of the headfor most of 66 2 g g the length of the slot, and then upwardly near theedge so that the peripheral-edge 46 is un-.' The tool illustrated inFigure '11 isbroken. shaped particularly for this screw head. Each lugl5 fits snugly in one of the slots 44 and the end face of the tool isrecessed as at 4'! to receive the curved upper surface of the screwhead.

A screw with a binding or fillister head 50 is shown in Figure 7. Thisscrew has a curved upper contour and a cylindrical side. The centralsurface area 52 is unrecessed so that it lies in the contour of the topand from it a plurality of slots, preferably four, extend radially, eachslot having parallel side walls and a bottom which slopes downwardly ina straight line away from the central area 52 to the periphery of thehead.

In each of the screw heads illustrated in the drawing, the bottoms ofthe slots make angles with the axis of the screw which are greater than45". This feature not only facilitates manufacture but is helpful incentering the driving tool.

Instead of making fiat-headed and oval-headed screws with slots stoppingshort of the peripheral edge of the head as shown in Figures 4, 5 and 6,I may extend the slots through so that they open out on the conicalunder face or shoulder of the screw as shown in Figures 8, 9 and 10.Figures 8 and 9 show a flat head similar to that shown in Figures 4 and5 except that the slots 58 have bottoms which slope down until theytation.

I claim: I 1. A screw head having a substantial unrecessed centralsurface portion, said head having a. plurality of grooves extendingradially a from. said central surface portion, 'each said groove havingparallel sidewalls and a bottom which slopes downward from the center ofthe head for rality of grooves extending radially outwardfrom saidcentral portion, each groove having parallel side walls and a straightbottom sloping outward and downward toward the periphery of the head.

4. A screw head having a convex top surface with an unrecessed centralportion, said head having four grooves therein extending radially fromsaid central portion and disposed in symmetrical relation around thehead with equiangular spacing between them, each said groove havingparallel side walls and a straight bottom sloping radially outward anddownward, whereby centering of a driving tool on'said head isfacilitated and a minimum removal of material from the head is secured.

5. A screw head having a substantial unrecessed surface portion, saidhead having four radial grooves extending symmetrically from saidcentral surface portion, each said groove having parallel side walls anda straight bottom starting flush with said central surface portion andsliping radially outward and downward therefrom at an angle of more than45 with the.

axis of the screw.

CLARENCE G. HOLT.

